1. Field of the Invention
The present invention relates to a liquid crystal display device and, in particular, to a liquid crystal display device which is excellent in red reproducibility, and is equipped with a white-emitting LED device as a backlight device employing a combination of a blue-emitting LED and red/green phosphors and also equipped with a color filter having red pixels which are capable of exhibiting excellent red color reproducing properties well matched with this backlight device. Further, the present invention relates to a color filter to be used in such a liquid crystal display device. In particular, the present invention is quite applicable to an on-vehicle liquid crystal display device.
2. Description of the Related Art
At present, an on-vehicle liquid crystal display device is in widespread use rapidly especially centering around a car navigation device and a rear seat monitor. In addition to that, there is a trend to mount a liquid crystal display device as an instrument panel in recent years. Where a liquid crystal display device is applied to the instrument panel, added values, which are quite different from the conventional analog meters, are provided.
In the case of the conventional on-vehicle liquid crystal display device such as a car navigation device, a rear seat monitor, etc., a cold cathode fluorescent lamp (CCFL), which is employed in ordinary liquid crystal display devices, has been employed as a backlight device. However, the cold cathode fluorescent lamp is accompanied with problems that it is poor in responsibility, weak in vibration and in shock, and adverse to environments due to the mercury contained in the cold cathode fluorescent lamp.
Further, a so-called ELV directive (End of Life vehicles directive) was put into force against vehicle components in October 2000 in the European Union. According to this regulation, it is stipulated to reduce the usage amount of Pb, Hg and Cr6+ to not more than 1000 pm and also to reduce the usage amount of Cd to not more than 100 pm in cars, buses and trucks to be registered in the EU markets starting from Jul. 1, 2003. This regulation aims at promoting the utilization, recycling and reclamation of waste matters of scrapped motor cars.
The on-vehicle display device is also one of the objects to be regulated by this regulation, so that the backlight device for these display devices is increasingly executed by making use of light-emitting diodes (LEDs) which are mercury-free in place of the conventional cold cathode fluorescent lamp where mercury is employed.
With respect to the LED backlight device, there are known a 3-wavelength white-emitting LED device where a 3-color LED light source consisting of a red LED light source, a green LED light source and a blue-emitting LED light source is employed (see Jpn. Pat. Appln. KOKAI Publication No. 2007-47781, for example), and a white-emitting LED device where the light to be emitted from a blue-based LED is color-mixed by passing it through a phosphor such as yttrium-aluminum-garnet (YAG), etc. Among them, the white-emitting LED device is widely employed in recent years as a small liquid display device to be used in mobile monitoring devices.
As far as the LED for the backlight device is concerned, since the three-color LED is low in cost merit in terms of individual variation and manufacturing cost, the white-emitting LED device is mainly used at present, so that the cold cathode fluorescent lamp that has been used as a backlight device for an on-vehicle liquid crystal display device is expected to be gradually replaced by the white-emitting LED device.
However, the employment of the white-emitting LED device as a backlight device is accompanied with a problem that since the white-emitting LED device does not exhibit an emission peak in a long wavelength region, the color reproducibility of the red display of liquid display device is prominently deteriorated. Whereas, in the case of the display to be mounted on a vehicle, it attaches importance very much to the red reproducibility as seen in the case of alarm display, etc. For this reason, there are great demands for an on-vehicle liquid crystal display device which is excellent in red reproducibility while making it possible to use, as a backlight device, an LED light source which is of high merit in terms of mercury-free.